The present invention relates generally to a device for removing excess carrier liquid on an image carrying member of image reproducing apparatus, and more particularly concerns a device for removing excess carrier liquid by using a specific carrier liquid removing roller member or belt member coupled to additional squeezing roller or vacuum source.
As a developing method for the latent images formed on the photoconductive drum, both dry developing methods and liquid developing methods have been used.
The liquid carrier used in the liquid developing method enables a fine dispersion of toner particles therein. Therefore, the liquid developing method is suitable for color image development requiring high-resolution images. Also, liquid development is suitable for color reproducing methods such as the image-on-image developing process, in which different color toner images are formed continuously on a photoconductive drum, because the scavengeless characteristic of liquid development compare to the dry developing process. However, when liquid developer is used, carrier liquid remains on the surface of a photoconductive member with toner particles. While the carrier liquid is necessary to transfer toner particles onto the surface of the photoconductive drum, excess carrier liquid remaining on the surface of the photoconductive member should be removed before the following transfer process, because the remaining carrier liquid contributes to a low transfer phenomenon of the toner particles to the copy paper and low fusing efficiency of the toner image on the copy paper. Also, excess liquid developer should be removed in order to prevent the discharge of vaporized liquid carrier to the outside environment of the machine. To remove the excess carrier liquid from the surface of the photoconductive member, various kind of excess carrier liquid removing devices have been utilized.
U.S. Pat. No. 4,286,039 discloses an image forming apparatus comprising a deformable polyurethane roller, which may be a squeezing roller or blotting roller, biased by a potential having a polarity the same as the polarity of the charged toner particles in a liquid developer. The bias on the polyurethane roller is such that it prevents streaking, smearing, tailing or distortion of the developed electrostatic image and removes much of the liquid carrier of the liquid developer from the surface of the photoconductor.
U.S. Pat. No. 4,299,902 discloses an image forming apparatus comprising an elastic roller which squeezes out and absorbs excess liquid developer. The elastic roller is comprised of a central roller, a porous elastic member wrapped around the roller, and an outermost elastic member with a plurality of penetrating pores. As the outermost elastic member, a net member having 100-300 mesh composed of a textile of monofilament fibers of polyamide, polyester, polypropylene, polyether, vinylon are disclosed.
U.S. Pat. No. 4,392,742 discloses a cleaning system for a liquid developer electrophotographic copier comprising a roller formed with a resilient material, such as a closed-cell elastomer, having externally exposed, internally isolated surface cells. During operation, the excess liquid on an imaging surface is absorbed by the cleaning roller. The cleaning roller is then compressed to squeeze out liquid from the roller, leaving the roller dry.
U.S. Pat. No. 4,878,090 discloses a development apparatus comprising a vacuum source which draws air around a shroud to remove excess liquid carrier from the development zone.
U.S. Pat. No. 4,879,197 discloses a pair of squeeze rollers for an electrophotographic machine comprising a metal roll with an elastomeric roller wrapped around the metal. The squeeze rollers remove excess developer from the photoreceptor.
U.S. Pat. No. 3,757,398 discloses a squeezing roller comprised of a thin layer of synthetic material with squeezes liquid from textile webs. As the synthetic material, polyurethane foam is disclosed.
U.S. Pat. No. 5,023,665 discloses an excess liquid carrier removal apparatus for an electrophotographic machine. The apparatus is comprised of an electrically biased electrode having a slit therein coupled to vacuum pump. The vacuum pump removes, through the slit in the electrode, liquid carrier from the space between the electrode and the photoconductive member. The electrical bias generates an electrical field so that the toner particle image remains undisturbed as the vacuum withdraws air and liquid carrier from the gap.
U.S. Pat. No. 4,607,947 discloses a circulating cleaning member comprising a multiplicity of spaced-apart openings or perforations. A surface of the cleaning member collects residues of toner from a surface to be cleaned.
U.S. Pat. No. 5,332,642 discloses a vacuum assisted dispersant reduction system. The system includes a vacuum pump and a biased roller coupled to a bias source which has same polarity with the toner charge. The biased roller includes a carrier liquid absorption material including polytetrafluoroethylene foam member. The patent also disclose capillary action to absorb the carrier liquid and the best surface characteristic of a surface layer as hydrophobic characteristic due to "surface tension".
JP-A 50-45645 discloses a carrier liquid squeezing system comprising a first squeezing roller contacted to a photoreceptor and second squeezing roller pressingly contacted to the first squeezing roller so as to squeeze the carrier liquid from the first squeezing roller. For the squeezing roller, sponge like materials such as polyurethane foam are disclosed.
JP-A 3-80274 discloses a carrier liquid squeezing system which is comprised of cylindrical foam roller and an uniform fine particle layer formed on the foam roller. The carrier liquid is removed by vacuum force generated by vacuum source coupled to a hollow portion of the cylindrical foam roller.
JP-A 3-145680 discloses a carrier liquid squeezing system which is comprised of rotatable hollow sponge roller, vacuum source coupled to a hollow portion of the cylindrical foam roller and cover member to cover a surface of the sponge roller portionally to enhance the vacuum force.
However, these carrier liquid removing devices unintentionally remove the toner particles partially with the excess carrier liquid therefrom. The lack of uniformity of toner -image concentration causes unacceptable or severe image defects in resulting toner image, especially in pictorial color image produced by color image reproducing techniques. In addition, the contacting-type excess liquid carrier removing device is sometimes deformed by mechanical or chemical stress during the image forming process. The deformed surface of the roller also results in a partial offset phenomenon sufficient to produce unacceptable or severely degraded image quality.
The offset toner particles on the surface of the carrier liquid removing roller cause reattachment of the toner particles to the surface of the photoconductive member, which also results in further image defects. Otherwise, the offset toner particles are drawn into apertures or openings of the absorbing roller and accumulated therein, causing a declining of vacuum power.
The references cited herein are incorporated by reference for their teachings.